The major players in the case may be dead, but the $1.6 billion Anna Nicole Smith inheritance battle still walks the courts of America like a legal zombie.

The latest twist came yesterday, when the federal appeals court in San Francisco ruled that the late Playboy model’s late billionaire husband, J. Howard Marshall, was mentally fit when he left nearly all of his fortune to his son E. Pierce Marshall — who is also dead.

The ruling comes after 15 years of legal wrangling that at one point reached the Supreme Court and is great news to Pierce Marshall’s widow and two sons, who now stand to inherit the money.

But they better live long if they hope to see it. Lawyers for the estate of Smith — who claims Marshall promised her more than $300 million — are not giving up and have vowed to drag the case back to the Supreme Court on new legal issues.

“It really is a unique decision,” said Kent Richland, a lawyer for Smith’s estate. “We have to take it farther.”

Pierce’s widow and two sons said they hope the legal battle is close to ending.

“Our only wish would be that Pierce were here to see his vindication,” the family said in a statement.

The decision — if it holds up — is bad news for Smith’s ex-boyfriend Larry Birkhead and their 3-year-old daughter Dannielynn. The child was named Smith’s heir in 2008 after she died of a drug overdose at 39 at a Florida hotel.

Birkhead and attorney Howard K. Stern were placed in charge of Smith’s estate.

Stern and two other people have pleaded not guilty to charges of conspiring to provide thousands of prescription pills to the former model before her death.

The convoluted dispute over J. Howard Marshall’s money has its roots in a Houston strip club where he met Smith. The two were wed in 1994 when he was 89 and she 26. Marshall died the next year and his will left his estate to his son.

Smith challenged the will in a Houston probate court, alleging the billionaire’s son illegally coerced his father to exclude the former Playboy model from sharing the estate. She also alleged that her husband promised to leave her more than $300 million above the $7 million in cash and gifts showered on her during their 14-month marriage.

While the probate case was pending in Houston, Smith filed for bankruptcy in Los Angeles, alleging in federal court filings that her husband promised her a large share of the estate.

In late 2000, the bankruptcy court awarded Smith $474.75 million, which a federal district court judge reduced to $89.5 million in 2002.

Between those two decisions, a jury in the Houston probate court ruled in March 2001 against Smith. The jury found the billionaire was mentally fit and under no duress when he wrote out a will that left everything to his son.

Since then, the two sides have been fighting over which court to obey.